Carp fish seasonal acclimatization induces a cyclical transcriptional modulation of several genes. Its most dramatic expression results in a concomitant structural rearrangement of the nucleolar components that phenotypically represents profound shifts in the level of ribosomal RNA synthesis. In connection with the recent studies that implicate CK2 in the control of rRNA synthesis in vertebrates, we characterized the cDNA of carp protein kinase CK2 beta subunit and assessed its transcriptional behavior in winter- and summer-acclimatized fish. We found a remarkable differential gene expression of CK2 beta subunit between summer- and winter-acclimatized carp which correlates with the modulatory pattern observed in rRNA transcription.